revise network integration and add support of futures
revise network integration and add support of futures

smoltcp 0.7 provides async/await waker support (https://github.com/smoltcp-rs/smoltcp/pull/394).
I followed the example implementation https://github.com/embassy-rs/embassy/tree/net/embassy-net
to add waker support in hermit-sys.

However, hermit-sys can be used in a multi-threaded applications.
Consequently, the implementation must be thread safed. In addition,
we still have an "network thread", which is wakeup by an interrupt.
The thread wakeups all waiting future. If no future is available,
the thread calls directly the IP stack.

hermitcore/rusty-hermit,hermitcore/rusty-hermit